1. Field Of The Invention
This invention relates to an emergency lighting device, more particularly to an emergency lighting device which is operable in the event of a power outage.
2. Description Of The Related Art
A conventional emergency lighting device is shown in FIG. 1. The conventional emergency lighting device includes a casing (10) which is fixed on a wall (20). A detecting unit (not shown) is installed inside the casing (10) and is connected electrically to a plug (11). The plug (11) is connected to an electric socket (19) so that the detecting unit can detect the presence of line power in the electric socket (19). When a power outage occurs, the detecting unit generates and transmits a signal to a driving unit (not shown) which is installed inside the casing and is connected electrically to the detecting unit. The driving unit enables a rechargeable battery (13) to supply the required power to activate the lamps (12). Referring to FIG. 2, a schematic block diagram of the circuit of the conventional emergency lighting device is shown. The detecting unit includes a rectifier unit (14) and a control unit (15). The plug (11) is connected electrically to the electric socket (19) (see FIG. 1) so that a sinusoidal alternating current line signal with a predetermined frequency, such as 110 V/60 HZ, 220 V/60 HZ, 100 V/50 HZ, etc., is transmitted to the rectifier unit (14). The rectifier unit (14) provides a direct current output via an output terminal (141). The output terminal (141) is connected electrically to the battery (13) and the control unit (15) so that the direct current output charges the battery (13) and is transmitted to the control unit (15). When the control unit (15) ceases to receive the direct current output from the rectifier unit (14), the control unit (15) enables the driving unit (16). The driving unit (16) is designed to be responsive to the intensity of the surrounding light so that the driving unit (16) permits the battery (13) to supply the required power to activate the lamps (12) via an output terminal (131) only upon the presence of weak surrounding light.
The drawback of the above-described conventional emergency lighting device is that a surge in the line signal may be transmitted from the electric socket to the lighting device immediately before the power outage occurs, thereby damaging the lighting device. Furthermore, the lighting device should be in constant connection with a socket (19), thereby limiting the place for installing the lighting device.